In this paper linear elastic fracture mechanics is used to evaluate the fracture toughness of sea ice, which was collected from Bohai Bay and researched experimentally in the recent 84/85 winter. The value of fracture toughness and its trend under different loading rate is analyzed. Not only the fracture toughness of mode I is discussed, but also the fracture criterion of II and combined mode is firstly investigated. If the rate is not too low, the critical stress intensity factor KIIC does not vary with the variation of stress intensity factor rate K̇II . Experimental results of sea ice under combined fracture mode coincide well with the criterion obtained from the strain energy density factor theorem. But this theorem cannot be employed so well to determine the orientation of crack propagating tendency.